This invention relates to the art of measuring blood parameters and more particularly pH and oxygen present in blood.
In a critical care setting, there is a need for measurement of various blood parameters. Included among these parameters are pH and oxygen. The values of these parameters are used in patient management. For example, both the pH content and the oxygen content are important parameters in the study of blood oxygen content. pH is an important parameter in studying some diseases such sickle cell anemia. Oxygen content is also an important parameter in the study of sickle cell anemia.
Both pH and oxygen blood parameters have been studied in the past by external means, wherein blood samples are withdrawn from a patient and studied externally of the body. However, there is concern in critically ill patients that blood withdrawal, even in small amounts, could present problems to a patient. Moreover, it is frequently desirable in studying such diseases as sickle cell anemia that an analysis be made in place during exercise.
It has been known to provide devices for use during in-dwelling measurement of various blood parameters. For example, U.S. Pat. No. 3,787,119 to Tybak discloses a catheter having a microlamp and a photosensitive element and other elements including a cup-like element for use in receiving blood and providing electrical output signals by means of wires extending through the catheter. Such construction could well present size limitations as well as stiffness limitations of the sensor carrier or catheter employed for incorporating suitable sensor wires.
The U.S. Pat. No. 3,814,081 to Morie discloses an optical measuring catheter employing fiber optic means for use in measuring oxygen saturation in blood, as well as blood pressure.
Whereas Rybak and Morie employ teachings of in-dwelling catheters which may be employed for measuring a plurality of blood parameters, there is no teaching of a device which can be employed for measuring both partial pressure of oxygen (PO.sub.2) as well as pH content of blood.
The U.S. Pat. No. 4,200,110 to Peterson et al. discloses a fiber optic pH probe wherein the probe includes an ion permeable membrane which encloses a guide containing solid material comprised of a hydrophilic copolymer having a pH sensitive dye attached thereto. The probe operates on the concept of optically detecting a change in color of the pH sensitive dye when excited by light. A phenol red dye is employed so that it absorbs light at a particular wavelength, on the order of 550 nm, with the amount of light being absorbed varying in dependence upon the pH level. There is no teaching, then, as to how the probe may also be employed for measuring oxygen partial pressure (pO.sub.2).
The U.S. patent to Peterson et al. U.S. Pat. No. 4,476,870 discloses a fiberoptic oxygen partial pressure (pO.sub.2) probe. This probe includes a hydrophobic gas permeable envelope which contains an adsorptive support which contains a fluorescent dye. Use of the probe for measuring partial pressure of gaseous oxygen in the bloodstream is based on the principle of dye fluorescent oxygen quenching. Thus, with the probe in place within a bloodstream, fluorescent dye is excited by light of a blue wavelength causing the dye to fluoresce at a green wavelength with the intensity of emitted light decreasing (quenching) with increasing levels of the partial pressure of gaseous oxygen in the bloodstream. There is no teaching in Peterson U.S. Pat. No. 4,476,870 of employing the same probe to also measure the pH content of the blood.
There is no teaching in the two Peterson patents, supra, by which features of the two probes could be combined together to provide a single probe for measuring pH and oxygen partial pressure with a single probe either simultaneously or in sequence. For example, if one employs the hydrophilic material containing the pH sensitive dye of Peterson U.S. Pat. No. (4,200,110) within the hydrophobic envelope in Peterson U.S. Pat. No. (4,476,870), the resultant probe would not be effective to sense pH content.